"Paul E. McKenney" [off-list ref] wrote:

quoted

but you can't trap this with a single counter increment in do_truncate:

 > 
 > 	CPU 0			CPU 1
 > 	----------		-----------
 > 				do_no_page
 > 	truncate

        i_size = new_i_size;

 > 	increment counter
 > 				read counter
 > 				->nopage

                                check i_size

 > 	vmtruncate
 > 				read counter again -> different so retry
 > 
 > thanks to the second counter increment after vmtruncate in my fix, the
 > above race couldn't happen.

 The trick is that CPU 0 is expected to have updated the filesystem's
 idea of what pages are available before calling vmtruncate,
 invalidate_mmap_range() or whichever.

i_size has been updated, and filemap_nopage() will return NULL.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>